If a creature is an astronaut if it likes mud and every pig likes mud, then every pig is an astronaut.
Saying that if a creature cannot fly then it is not an astronaut is the same as saying that all astronauts fly. Since all pigs are astronauts, pigs can fly.
To fine the percentage decrease, we use the formula change/original x 100. In this case, the change is $11000-$9799=$1201 while the original is $11000. So 1201/11000 x 100 = 10.9% ≈ 11%